1. Field of the Invention
The present invention relates to a vessel propulsion apparatus including an engine (internal combustion engine) as a drive source.
2. Description of the Related Art
An example of a vessel propulsion apparatus is an outboard motor. An outboard motor includes, for example, an engine, a propeller, and a driving force transmitting mechanism that transmits a driving force of the engine to the propeller. The driving force transmitting mechanism includes a shift mechanism that switches transmission of a torque of the engine to the propeller. The shift mechanism switches a shift position of the outboard motor. The shift position includes “forward” to convert the rotation of the engine into forward-traveling rotation (forward rotation) of the propeller, “backward” to convert the rotation of the engine into backward-traveling rotation (reverse rotation) of the propeller, and “neutral” not to transmit the rotation of the engine to the propeller. Provision of this shift mechanism enables the rotation directions of the propeller and the propeller shaft to be switched between the forward rotation direction and the reverse rotation direction while the engine always rotates in one direction.
When a vessel operator switches the shift position from forward to backward in a state in which a vessel equipped with an outboard motor travels forward at a high speed, even though a driving force to be transmitted from an engine to a propeller shaft is a torque in a reverse rotation direction, the propeller is rotated in the forward rotation direction by a water flow generated by inertia acting on the vessel. Normally, this operation method is not recommended from the viewpoint of vessel stability and engine protection. If this operation is performed, however, a torque to reversely rotate the crankshaft of the engine is input from the propeller. If a torque thus reversely input from the propeller exceeds the driving force of the engine, the crankshaft reversely rotates. In particular, in an outboard motor having an exhaust port in the water, due to reverse rotation of the crankshaft, water may be suctioned from the exhaust port and enter the inside of the engine.
Therefore, it has been proposed that reverse rotation of the engine is detected and informed to a user, the engine is stopped, or the power transmission path is blocked by forcibly switching the shift position to neutral.
For example, in the conventional technology described in US 2003/0106364 A1, reverse rotation of the engine is detected based on a pulse output corresponding to rotation of the crankshaft, and when reverse rotation of the engine is detected, ignition and fuel injection are stopped. In the conventional technology described in US 2008/0268726 A1, reverse rotation of the crankshaft is detected based on pulses output corresponding to rotations of the crankshaft and the cam shaft, and when reverse rotation is detected, the shift position is forcibly shifted to neutral.
On the other hand, in the conventional technology described in US 2011/0318977 A1, reverse rotation is detected by monitoring a pressure change of an oil pump or a cooling water pump that is driven by rotation of the crankshaft. For example, a minimum oil pressure Pmin is set, and when the minimum oil pressure Pmin is exceeded at the time of shift switching, it is determined that oil is not supplied by the oil pump, and based on this, it is determined that the crankshaft interlocked with the pump drive shaft is rotating in the reverse direction.